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Active and passive source data from two seismic experiments within the interdisciplinary project TIPTEQ (from The Incoming Plate to mega Thrust EarthQuake processes) were used to image and identify the structural and petrophysical properties (such as P- and S-velocities, Poisson's ratios, pore pressure, density and amount of fluids) within the Chilean seismogenic coupling zone at 38.25°S, where in 1960 the largest earthquake ever recorded (Mw 9.5) occurred. Two S-wave velocity models calculated using traveltime and noise tomography techniques were merged with an existing velocity model to obtain a 2D S-wave velocity model, which gathered the advantages of each individual model. In a following step, P- and S-reflectivity images of the subduction zone were obtained using different pre stack and post-stack depth migration techniques. Among them, the recent prestack line-drawing depth migration scheme yielded revealing results. Next, synthetic seismograms modelled using the reflectivity method allowed, through their input 1D synthetic P- and S-velocities, to infer the composition and rocks within the subduction zone. Finally, an image of the subduction zone is given, jointly interpreting the results from this work with results from other studies. The Chilean seismogenic coupling zone at 38.25°S shows a continental crust with highly reflective horizontal, as well as (steep) dipping events. Among them, the Lanalhue Fault Zone (LFZ), which is interpreted to be east-dipping, is imaged to very shallow depths. Some steep reflectors are observed for the first time, for example one near the coast, related to high seismicity and another one near the LFZ. Steep shallow reflectivity towards the volcanic arc could be related to a steep west-dipping reflector interpreted as fluids and/or melts, migrating upwards due to material recycling in the continental mantle wedge. The high resolution of the S-velocity model in the first kilometres allowed to identify several sedimentary basins, characterized by very low P- and S-velocities, high Poisson's ratios and possible steep reflectivity. Such high Poisson's ratios are also observed within the oceanic crust, which reaches the seismogenic zone hydrated due to bending-related faulting. It is interpreted to release water until reaching the coast and under the continental mantle wedge. In terms of seismic velocities, the inferred composition and rocks in the continental crust is in agreement with field geology observations at the surface along the proflle. Furthermore, there is no requirement to call on the existence of measurable amounts of present-day fluids above the plate interface in the continental crust of the Coastal Cordillera and the Central Valley in this part of the Chilean convergent margin. A large-scale anisotropy in the continental crust and upper mantle, previously proposed from magnetotelluric studies, is proposed from seismic velocities. However, quantitative studies on this topic in the continental crust of the Chilean seismogenic zone at 38.25°S do not exist to date.
Following work is embedded in the multidisciplinary study DESERT (DEad SEa Rift Transect) that has been carried out in the Middle East since the beginning of the year 2000. It focuses on the structure of the southern Dead Sea Transform (DST), the transform plate boundary between Africa (Sinai) and the Arabian microplate. The left-lateral displacement along this major active strike-slip fault amounts to more than 100 km since Miocene times. The DESERT near-vertical seismic reflection (NVR) experiment crossed the DST in the Arava Valley between Red Sea and Dead Sea, where its main fault is called Arava Fault. The 100 km long profile extends in a NW—SE direction from Sede Boqer/Israel to Ma'an/Jordan and coincides with the central part of a wide-angle seismic refraction/reflection line. Near-vertical seismic reflection studies are powerful tools to study the crustal architecture down to the crust/mantle boundary. Although they cannot directly image steeply dipping fault zones, they can give indirect evidence for transform motion by offset reflectors or an abrupt change in reflectivity pattern. Since no seismic reflection profile had crossed the DST before DESERT, important aspects of this transform plate boundary and related crustal structures were not known. Thus this study aimed to resolve the DST's manifestation in both the upper and the lower crust. It was to show, whether the DST penetrates into the mantle and whether it is associated with an offset of the crust/mantle boundary, which is observed at other large strike-slip zones. In this work a short description of the seismic reflection method and the various processing steps is followed by a geological interpretation of the seismic data, taking into account relevant information from other studies. Geological investigations in the area of the NVR profile showed, that the Arava Fault can partly be recognized in the field by small scarps in the Neogene sediments, small pressure ridges or rhomb-shaped grabens. A typical fault zone architecture with a fault gauge, fault-related damage zone, and undeformed host rock, that has been reported from other large fault zones, could not be found. Therefore, as a complementary part to the NVR experiment, which was designed to resolve deeper crustal structures, ASTER (Advanced Spacebourne Thermal Emission and Reflection Radiometer) satellite images were used to analyze surface deformation and determine neotectonic activity.